Each vehicle carrying an internal-combustion engine has a fuel tank that stores fuel. The fuel tank is provided with a fuel level sensor that detects a level of fuel therein. Once the fuel level sensor malfunctions, it is impossible to detect a fuel level. This causes troubles for vehicle normal operation.
Then, JP2007-10574A discloses an invention of a trouble diagnostic device configured to diagnose troubles of a fuel level gage that detects a fuel level. This trouble diagnostic device calculates a fuel consumption by integrating fuel injection amounts that have been injected from a fuel injection valve; and when the fuel injection amount integrated value does not correlate to a fuel level gage output (change in fuel level), the fuel level gage is diagnosed to have a malfunction.
This trouble diagnostic device can accurately diagnose a malfunction of the fuel level gage.